1. Field of the Invention
The invention relates to a hybrid vehicle that has an internal combustion engine including in-cylinder injection valves and port injection valves, and an electric motor, as driving sources (power sources), and runs while controlling output torque of these driving sources. The invention also relates to a method of controlling the hybrid vehicle.
2. Description of the Related Art
A hybrid vehicle is equipped with an internal combustion engine and an electric motor, as driving sources that generate driving force for running the vehicle. Namely, the hybrid vehicle runs with torque generated by at least one of the engine and the electric motor and transmitted to a drive shaft connected to driving wheels of the vehicle.
In some cases, the hybrid vehicle is equipped with an internal combustion engine including a fuel injection valve (i.e., in-cylinder injection valve) that directly injects fuel into a combustion chamber of each cylinder, and a fuel injection valve (i.e., port injection valve) that injects fuel into an intake port that communicates with the combustion chamber. One type of the hybrid vehicle equipped with the engine including the in-cylinder injection valve and the port injection valve for each cylinder is adapted to run in a selected one of a port injection drive mode, an in-cylinder injection drive mode, and a both-injector drive mode, in order to make various diagnoses of malfunctions (see, for example, Japanese Patent Application Publication No. 2005-226553 (JP 2005-226553 A). In the port injection drive mode, the total amount of fuel supplied to the engine is injected from the port injection valve. In the in-cylinder injection mode, the total amount of fuel supplied to the engine is injected from the in-cylinder injection valve. In the both-injector drive mode, fuel is injected from both the in-cylinder injection valve and the port injection valve.
One type of known hybrid vehicle has a system that determines engine required power, based on torque determined according to the amount of accelerator operation by the user (namely, user-requested torque required to be applied to the drive shaft of the vehicle). Furthermore, the system of the known hybrid vehicle controls the engine so that the engine generates power that satisfies the engine required power, while assuring the optimum operating efficiency, and controls the electric motor so that the motor generates output torque that makes up for a shortage of output torque of the engine transmitted to the drive shaft, relative to the user-requested torque.
When the user-requested torque is small (accordingly, the user-requested power is small), and therefore, the engine is not able to operate at an efficiency equal to or higher than a given efficiency (namely, when an engine operation stop condition is satisfied), the system of the known hybrid vehicle stops operation of the engine, so that the user-requested torque is satisfied or provided solely by output torque of the electric motor. In addition, when the user-requested torque increases (accordingly, the user-requested power increases) in a condition where the operation of the engine is stopped, and therefore, the engine becomes able to operate at an efficiency equal to or higher than the given efficiency (namely, when an engine start condition is satisfied,) the system of the known hybrid vehicle starts the engine, so that the user-requested torque is satisfied or provided by output torque of the engine and output torque of the motor. Thus, since the engine is stopped and started in this manner, or intermittently operated, the above operation of the engine is also called “intermittent operation or engine intermittent operation”.
In the engine as described above, it is desirable to make a determination (in-cylinder injection valve abnormality determination) as to whether an abnormality occurs to the in-cylinder injection valve, and make a determination (port injection valve abnormality determination) as to whether an abnormality occurs to the port injection valve. The engine needs to be operated in the above-mentioned in-cylinder injection drive mode in order to make an in-cylinder injection valve abnormality determination, and the engine needs to be operated in the above-mentioned port injection drive mode in order to make a port injection valve abnormality determination.
On one hand, if the engine is kept operating in the port injection drive mode in a condition where the load of the engine is relatively high, the temperature in the vicinity of a fuel injection hole (nozzle) of the in-cylinder injection valve becomes excessively high. Accordingly, it is difficult to make a port injection valve abnormality determination when the engine is in a high-load condition.
In a condition where the load of the engine is relatively low, on the other hand, the engine can be kept operating in the port injection drive mode or the in-cylinder injection drive mode, over a relatively long period of time though there is a limit to the period. Accordingly, it is preferable to make an in-cylinder injection valve abnormality determination and a port injection valve abnormality determination (these abnormality determinations will be collectively called “injection valve abnormality determinations”), in a condition where the load of the engine is relatively low.
However, in the hybrid vehicle as described above, the operation of the engine is stopped under control for the intermittent operation when the load of the engine is low, which may result in a significant reduction in chances of making injection valve abnormality determinations. Further, in a hybrid vehicle in which the engine is stopped under control for the intermittent operation when an engine stop condition different from the above-described engine stop condition is satisfied, too, since injection valve abnormality determinations cannot be made while the operation of the engine is stopped, there arises a delay in making the injection valve abnormality determinations.